1. Field of the Invention
The present invention relates to an optical pickup for playing back or reading an optical disk and, more particularly, to a method of adjusting optics of an optical pickup using a light-emitting-and-receiving device comprising a semiconductor substrate on which a light-emitting portion and a light-receiving portion are integrally formed.
2. Description of the Related Art
The prior art optical pickup which is for use with an optical disk and uses a light-emitting-and-receiving device is described in U.S. Pat. No. 4,823,331. The construction of the prior art optical pickup is particularly shown in FIG. 1.
In FIG. 1, the optical pickup is generally indicated by reference numeral 1. This pickup 1 includes a light-emitting-and-receiving device 2 (described later) and an objective lens OL disposed between the device 2 and an optical disk D. This lens OL is held by a support mechanism (not shown) so as to be capable of moving in the tracking direction TRK and also in the focusing direction FCS. The optical disk D is rotated by a driving source (not shown).
The light-emitting-and-receiving device 2 is constructed as shown in FIGS. 1 and 2. In particular, a prism 7 and a photodiode device 5 are fixedly mounted on a semiconductor substrate 4. A laser diode device 8 is securely mounted on the photodiode device 5. A first array of photodetectors PD1 and a second array of photodetectors PD2 are mounted on the surface of the semiconductor substrate 4 on which the prism 7 is mounted.
As shown in FIG. 2, the prism 7 has an inclined surface 7a which is tilted, for example, at an angle of .theta. to the bottom surface of the prism 7. Preferably, this angle .theta. is 45 degrees. The laser diode device 8 has a laser light exit portion 8a to which the inclined surface 7a is disposed substantially in an opposite relation. The inclined surface 7a reflects the light beam coming out of the laser light exit portion 8a toward the objective lens OL. The inclined surface 7a is a translucent surface through which the light beam reflected off the disk D is transmitted. The inclined surface 7a has a totally reflective surface 7b opposite to the surface held on the semiconductor substrate 4.
A light-receiving portion 5a for monitoring the laser light is formed on the photodiode device 5. This light-receiving portion 5a receives the laser light emerging from the rear side of the laser diode device 8 and detects the amount of beam coming out of the laser diode device.
A translucent membrane 6 is formed on the first array of photodetectors PD1. The membrane 6 transmits a part of the light beam transmitted through the inclined surface 7a of the prism 7; the remaining part is reflected by the membrane 6. The beam transmitted through the membrane 6 is guided to the first array of photodetectors PD1.
Referring again to FIG. 1, the light-emitting-and-receiving device 2 has a casing 3 which is composed of a substrate 3a, four side plates 3b, and a window glass 3c. The substrate 3a is positioned opposite to the window glass 3c which consists, for example, of transparent glass plate.
In the operation of the optical pickup 1 constructed in this way, the light beam L emitted from the laser diode device 8 is reflected by the inclined surface 7a of the trapezoidal prism 7 and is passed through the objective lens OL. During this process, the light is refracted by the action of the objective lens OL and focused onto the recording surface of the optical disk D. The light returning from the recording surface of the disk D travels to the inclined surface 7a of the prism 7 again via the objective lens OL.
A part of the returning light enters into the prism 7 from the inclined surface 7a of the prism 7. As shown in FIG. 3, a part of the returning light transmitted through the inclined surface 7a passes through the translucent membrane 6 and enters the first array of photodetectors PD1.
The remaining part of the returning light transmitted through the inclined surface 7a is reflected off the translucent membrane 6, is reflected by the totally reflective surface 7b, and enters the second array of photodetectors PD2.
Appropriate calculations are performed on the output signals from those of the photodetectors PD1 of the first array which receive the light and on the output signals from the other photodetectors PD1. In this way, servo signals necessary for focusing and tracking are obtained.
In the optical pickup 1 of this construction, adjustment of optics of the light-emitting-and-receiving device in a radial direction of the optical disk, i.e., an adjustment of the position at which the pickup is mounted, is made by mechanically mounting the light-emitting-and-receiving device relative to the reference position of the pickup. On the other hand, in the track direction of the optical disk, the position of the light-emitting-and-receiving device is not adjusted. The position in the track direction is determined by the accuracy of the mechanism.
Consequently, the accuracies at which the light-emitting-and-receiving device is mounted in the radial direction and in the tangential direction of the optical disk are affected by the assembly accuracy of the optical pickup and by the mounting accuracies of the optical elements in the light-emitting-and-receiving device. In some cases, the optical axis deviates because of errors in the position at which the pickup is mounted.